The present invention relates to a three-dimensional shape detecting device for detecting the three-dimensional shape of a subject by use of an optical beam, an image capturing device employing the three-dimensional shape detecting device, and a three-dimensional shape detecting method.
As a three-dimensional shape detecting device designed to project a slit beam onto a subject, capture an image of the subject (onto which the slit beam is projected) with an image capturing device, and detect the three-dimensional shape of the subject based on image data obtained by the image capturing device, the following device disclosed in Japanese Patent Provisional Publication No.HEI07-318315 is well known.
The three-dimensional shape detecting device is configured to transform an optical beam emitted by a light source into a slit beam, split the slit beam into two slit beams using a half mirror, and project the two slit beams onto a subject. The three-dimensional shape detecting device captures an image of reflecting positions of the two slit beams being reflected by the subject (hereinafter referred to as “loci of the slit beams”) and figures out positions (relative to the three-dimensional shape detecting device) regarding points (pixels) in the captured image corresponding to the loci of the slit beams. Further, when the subject is a sheet-like object, the three-dimensional shape of the whole subject is estimated by the three-dimensional shape detecting device. Consequently, the three-dimensional shape of the subject is determined by the three-dimensional shape detecting device.
In the above three-dimensional shape detecting device, a slit beam generated by a light source unit is split into two slit beams by a half mirror. In this case, two slit beams having the same spread angle are emitted toward the subject, by which two slit beams of substantially the same length are projected on the subject.
Such a configuration involves the following disadvantages. For example, assuming that a point source of light having limited total emission power is used for the light source unit, half the total emission power of the light source unit is distributed to each of the two slit beams due to the two-way splitting by the half mirror. Such slit beams, sharing the power half-and-half, may be insufficient for achieving sufficient luminance of the loci necessary for precise image reading.
The above example will be explained below more concretely. Assuming that a small-sized light source used for the above three-dimensional shape detecting device for emitting an optical beam is a laser diode having a rated output (total emission power) of 1 mW, when a laser beam emitted by the laser diode is transformed into a slit beam of a spread angle of 48 degrees, the power of the slit beam per unit angular width is approximately 21 μW/degree. Since a slit beam from the light source is split into two slit beams by a half mirror in the above three-dimensional shape detecting device, the power of each slit beam equals half the aforementioned power (approximately 10 μW/degree).
When a slit beam is projected onto white paper placed 330 mm away, illumination intensity on the paper is approximately 1320 lux in the case where only one slit beam is projected onto the paper. Meanwhile, in the case where a slit beam is split into two slit beams, illumination intensity caused by each slit beam is approximately 660 lux. Incidentally, this explanation assumes that the slit beam is a red laser beam having a wavelength of 650 nm, 1 W=73 lumens, and the width of the slit beam is 0.2 mm. In places where the illumination intensity is 500-1000 lux (average room illumination), the difference of luminance between the paper and the loci of the two slit beams is small, by which the recognition or discrimination of the loci from the image data of the subject becomes difficult.
In order to realize reliable recognition of the loci of the slit beams, a light source of higher total emission power has to be employed. Increasing the power of the light source is accompanied by high power consumption, replacement of components related to the light source, a higher price of the device, and enlargement of the device.